The addition of paraffin wax (100 ppm) to polyesters has been known for many years to prevent air inhibition of the open surface of mouldings on cure (B.P.713,332). More recently a need has arisen on environmental grounds to reduce the evaporation of styrene monomer from the surface of a laminate in the interval between lay-up and cure. This can be achieved by the incorporation of higher levels of paraffin wax, e.g. 1000 ppm, but this concentration of wax can have several drawbacks:
(a) wax can separate from the liquid resin when it is stored at low temperatures, PA1 (b) the layer of wax which comes to the surface can interfere with the adhesion between one layer of laminate and the next, especially where there is a delay between lay-up and cure and the surface is resin-rich. PA1 (a) reduce styrene emission from laminates, and PA1 (b) prevent air inhibition of the surface of the laminate.
In order to overcome these disadvantages, it has been proposed to incorporate small quantities of a straight chain hydrocarbon, e.g. n-octane or the use of a surfactant such as polyoxyethylene sorbitan fatty acid esters (German Offenlegungsschrift No. 2554930).
Neither of these methods has been particularly successful. For example 2% n-octane lowers the heat deflection temperature of the cured resin and imparts a milky appearance to the laminate.
U.S. patent application No. 63134 filed Aug. 3, 1979 by the present inventor is also directed to this problem of enabling higher quantities of wax to be added without incurring the abovementioned disadvantages. There, a terminally unsaturated compound capable of taking part in the cross-linking reaction is included to allow more wax to be incorporated in the composition. There is a disclosure, by way of example, of the use of an .alpha.-unsaturated olefine having 10 carbon atoms as such a compound.
Whilst this method works well with many resins, our results now show that for some unsaturated polyester resins based on halogenated acids such as chlorendic acid, the effect is not so marked.